The tech sector is filled with fresh technologies that are disrupting and reshaping older markets. The cloud, cybersecurity, fintech, and semiconductor markets host many of those top stocks.

All four markets will expand as companies and consumers move more data online: Cloud services will host that data, cybersecurity services will protect it, fintech services will leverage it to replace traditional banking services, and all that computing power will spark fresh demand for more powerful chips.

A visualization of networking connections across the globe.

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Let's take a look at four of my favorite stocks from those four industries -- Amazon (AMZN 0.22%), Palo Alto Networks (PANW 0.72%), Square (SQ 0.56%), and ASML Holding (ASML 2.39%) -- and why they're still excellent long-term investments.

1. Amazon: The cloud king

Amazon Web Services (AWS) controlled 31% of the global cloud infrastructure market in the second quarter of 2021, according to Canalys, making it the world's largest cloud platform. It established an early mover's advantage in that market, and its scale enables it to generate consistent profits, while most of its smaller rivals remain unprofitable.

Amazon's AWS revenue rose 35% year over year to $28.3 billion in the first half of 2021 and accounted for 12% of its top line. However, the segment's operating profit increased 30% to $8.4 billion and accounted for 50% of Amazon's total operating income -- so AWS' higher-margin revenue is supporting the expansion of Amazon's lower-margin retail marketplaces.

Those two growth engines make Amazon a great investment on both the e-commerce and cloud platform markets, and this FAANG stock still looks reasonably valued at just over 50 times forward earnings.

2. Palo Alto Networks: A balanced cybersecurity leader

Palo Alto Networks is a market leader in on-site firewall appliances. Over the past several years, it's expanded its ecosystem with cloud-based services and AI-powered platforms to counter new threats.

More than three-quarters of the Fortune 100 companies use Palo Alto's cloud-based cybersecurity services, and it generated 28% of its revenue from its NGS (next-generation security) cloud and AI platforms last year.

Palo Alto's revenue, billings, and adjusted earnings growth all accelerated in fiscal 2021, and it expects its revenue to rise another 24%-25% this year, with 16%-18% earnings growth.

Palo Alto isn't growing as rapidly as its cloud-native rival CrowdStrike (CRWD 1.30%), but its stock is more reasonably valued at 65 times forward earnings and 11 times this year's sales. CrowdStrike trades at nearly 400 times forward earnings and 47 times this year's sales.

Palo Alto's rare balance of growth and value makes it one of my favorite cybersecurity stocks, and it could have plenty of room to run as it expands its NGS services to counter new cybersecurity threats.

3. Square: The diversified fintech player

Square is one of the world's boldest and most innovative fintech companies. It initially turned phones and tablets into POS (point-of-sale) systems with dongles and apps, then expanded its ecosystem with services for processing transactions, handling payroll services, analyzing data, and selling products online.

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Square also launched peer-to-peer payments for consumers through its Cash App, which it subsequently expanded into a personal finance platform for free stock trades and Bitcoin (BTC -0.28%) purchases. It also recently agreed to buy Afterpay to add "buy now, pay later" services to its ecosystem and challenge traditional credit card companies.

Square's boldness paid off during the pandemic last year when its surging Bitcoin sales offset the slower growth of its seller-based services. Analysts expect its revenue and adjusted earnings to more than double this year, then decelerate next year as year-over-year comparisons normalize.

Square's stock isn't cheap at 113 times forward earnings. But if you believe it will profit from the disruption of traditional banks and the rise of Bitcoin, it could be a great long-term investment.

4. ASML: The semiconductor linchpin

Lastly, the Dutch semiconductor equipment maker ASML remains my top chipmaking stock because it dominates a key part of the supply chain. ASML produces photolithography machines that etch circuit patterns onto silicon wafers. It faces some competition in the lower-to-mid-range markets, but it dominates the market for high-end EUV (extreme ultraviolet) systems.

Chip foundries like Taiwan Semiconductor Manufacturing, Samsung, and Intel all use ASML's EUV machines to manufacture their smallest semiconductors. ASML only ships a few dozen EUV machines every year, but they accounted for 59% of its net bookings last quarter.

ASML's dominance of the EUV market gives it tremendous pricing power, and its gross margins have consistently expanded over the past several years. Analysts expect its revenue and earnings to grow 40% and 64%, respectively, this year, followed by more moderate growth next year.

ASML still looks reasonably valued at 45 times forward earnings, and it could command an even higher premium as the global chip shortage drags on and highlights the growing need for its EUV systems.